A machine tool such as a lathe includes a main spindle. The main spindle holds a piece to be processed (referred to a workpiece hereinafter) such as a round bar which extends from the tip of the main spindle. The machine tool processes the workpiece by rotating the workpiece about its shaft center and by contacting a tool such as a tool bit or cutting tool to the workpiece. The tool is moved by a feeder. Then, a controller controls the rotation and/or axial movement of the workpiece, and the movement of tools by the feeder.
The tool is moved in relation to the rotation of the workpiece to form a portion radially eccentric from the shaft center of the workpiece (referred to an eccentric portion hereinafter) in the workpiece by such a machine tool, (See, Patent Literature 1: JP 2002-066802A, for example).
In the turning process for the eccentric position by the lathe disclosed in Patent Literature 1, it is necessary to control a NC lathe with a complicated program which uses positional data obtained by calculating the positions of the tool point by point.
The present disclosure is made in light of the above, and a main object of the present disclosure is to provide a machine tool and a method for processing by the machine tool which can process an eccentric shape or portion with simple settings.